How about adding a field for Original Language or Country of Origin, or both.

Where you have a Type set to Manga, Manhua or Manhwa, or even OEL it is relatively easy to tell the Language or Country of Origin; however where the type is Artbook, Doujinshi, Drama CD, or Novel it becomes more problematic.

Before anyone turns around and says tht you could infer it from the Artist, Author or Original Publisher fields that would only work if they where always filled in.

Note
I include the Doujinshi amongst the ones that would be difficult to identify the Origin as it seems to have been used as a catch-all term regardless of the Language or Country of Origin.

I agree with this. Origin should be a separate field than type of media. Many of the things marked as "OEL" aren't really "original English language", either. It's just a catch-all for anything not from Japan, Korea, or China, and that bothers me.